The Lubbock Lake site, on the Southern High Plains of Texas, contains one of the most complete and best-dated late Quaternary records in North America. A total of 117 14C dates arc available from the site, determined by the Smithsonian and SMU Laboratories. Of these dates, 84 have been derived from residues (humin) and humates (humic acids) of organic-rich marsh sediments and A horizons of buried soils. Most of the ages are consistent with dates determined on charcoal and wood, and with the archaeologic and stratigraphic record. The dates on the marsh sediments are approximate points in time. Dates from the top of buried A-horizons are a maximum for burial and in many cases are close to the actual age of burial. Dates from the base of the A-horizons are a minimum for the beginning of soil formation, in some cases as much as several thousand years younger than the initiation of pedogenesis. A few pairs of dates were obtained from humin and humic acid derived from split samples; there are no consistencies in similarities or differences in these age pairs. It also became apparent that dates determined on samples from scraped trench walls or excavations that were left open for several years are younger than dates from samples taken from exactly the same locations when the sampling surfaces were freshly excavated.
ABSTRACT. Between 1984 and 1995 over 450 organic samples were collected from monuments built during the Old and Middle Kingdoms. The most suitable samples were selected for dating. The purpose was to establish a radiocarbon chronology with samples from secure context and collected with the careful techniques required for 14 C samples. This chronology is compared to the historical chronology established by reconstructing written documentation.
Data on the depth distribution of the major atmospheric gases and the abundance of gaseous 12CO2, 13CO2, and 14CO2 in the subsoil unsaturated zone have been obtained from several sites in the western Great Plains of the United States. Sample profiles range from land surface to depths of 50m. Although each site must be considered on an individual basis, several general statements can be made regarding the profiles. 1) Diffusion of these gaseous molecules through the unsaturated zone is an important transport mechanism. 2) As predicted by diffusion theory, depth profiles of the various isotopic species of CO2 differ substantially from one another, depending on individual sources and sinks such as root respiration and oxidation of organic carbon at depth. 3) In general, post-bomb (> 100% modern) 14C activities are not observed in the deep unsaturated zone, in contrast to diffusion model predictions. 4) In spite of generally decreasing 14C activities with depth, absolute partial pressures of 14CO2 in the subsoil unsaturated zone are 1–2 orders of magnitude higher than the partial pressure of 14CO2 in the atmosphere.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.